It is generally known to increase the shelf life of liquid products by killing germs and/or spores through heating and/or by inactivating enzymes.
The patent specification EP 1 487 240 B1 describes in this respect an apparatus in which an alternating current field is generated between pairs of electrodes arranged transversely to the flow direction of the product on the inner side of a treatment channel. The cross-section of the channel is configured for a laminar flow so as to cause the least possible shear in the product. This arrangement allows a particularly gentle treatment and is suitable, for example, for mixed products containing fruit pieces.
However, as regards the structural design and the application of this arrangement, problems arise, since the necessary energy input depends on the electric conductance of the product, the flow behavior of the product in the channel and the product temperature as well as on the clearance between the alternating current electrodes. This clearance influences, in turn, the flow behavior of the product. In the case of high conductance values and high product temperatures, it may be necessary to increase the spacing between the electrodes to such an extent that the product flow cannot be controlled in the desired manner. This can result, for example, in non-uniform heating of the product and/or in undesirable depositions in the treatment channel, a so-called fouling effect.
Since the product normally passes through a plurality of heating stages and since the electrode spacing can, for the above-mentioned reasons, sometimes not be adapted to the respective temperature ranges that are to be covered, individual heating stages have to be supplied by separate alternating current generators which are configured for the temperature range in question. This entails a substantial investment in the equipment used.
In addition, many products can be heated more uniformly and more efficiently, when a shear occurs in the products at high flow velocities. It can thus be avoided that the quality of the product, in particular color, flavor, protein content and consistency, degrades essentially in comparison with the original product. The known apparatuses are, however, not suitable for generating adequately strong and/or turbulent flows in a satisfactory manner.